WASHINGTON — Speaker John A. Boehner has been a luminary in the anti-abortion movement since he was a little-known Ohio state lawmaker, and is widely viewed as the most passionate opponent of abortion ever to wield the speaker’s gavel.

Yet abortion politics are suddenly posing the greatest threat to his speakership since he ascended to that position four years ago.

Conservatives on his right flank are questioning Mr. Boehner’s resolve to stand up to President Obama over federal funding for Planned Parenthood, and their agitation is so great, they are mulling a challenge to the speaker’s control of the House.

“It’s unfortunate that sometimes Republicans are self-destructive,” said Representative John L. Mica, Republican of Florida, who has served in the House for over two decades. “I would think the speaker can survive, but some have made it an election issue, and that puts members on the spot. So there are no guarantees. A small number of people can do a lot of damage.”

Those pressuring Mr. Boehner want him to agree to a strategy of removing all federal money for Planned Parenthood in a short-term spending bill to keep the government operating, an approach that would almost certainly fail in the Senate. Without a basic bill to keep the government running for the rest of the year, the lights would go out for a second time since Republicans took control of the House in 2011.

Mr. Boehner now faces an excruciating choice. He could follow the pragmatic approach embraced by Senator Mitch McConnell of Kentucky, the majority leader, to keep the government open and take on the Planned Parenthood fight later — a choice that could lead to an embarrassing challenge to the speaker. Or he could fling himself headfirst into yet another spending showdown in which conservatives have little chance of prevailing.

Image

Mr. Boehner at the Republican Party headquarters in Washington on Thursday.CreditZach Gibson/The New York Times

Anti-abortion groups view the struggle with unease. “He has consistently been there for the pro-life movement,” said Michael Gonidakis, the head of the Ohio chapter of Right to Life, which has had a close relationship with Mr. Boehner for decades. “I think standing up to Planned Parenthood will solidify his leadership. I am hoping that enough of his members will convince him to do that.” But, he added, “no one in the pro-life movement is interested in replacing the speaker.” Few in the movement seem to support a government shutdown, either.

Congress has until Sept. 30 to find a way to avoid a shutdown, and there is great division among House Republicans on how to proceed. “Before the plane takes off, you better know how, when and where to land it,” said Representative Charlie Dent, Republican of Pennsylvania. “Right now, there is no plan, and the plane is on the runway, engines revving.”

Members of the House have been preoccupied with the arrival of Pope Francis in Washington next week and the intrigue around Mr. Boehner’s future. It seems increasingly likely that Congress will not turn to the spending issue until the last week of September.

“We have no discussions of how to keep the government open just eight legislative days from now,” Representative Steny H. Hoyer of Maryland, the Democratic whip, said on the House floor Wednesday.

For Mr. Boehner, there is a stark incongruity. One of 12 children, Mr. Boehner has taken a far more activist position on abortion than on any other policy matter that animates Republicans. He has won numerous awards from anti-abortion groups, marched in an anti-abortion rally in Washington and made dismantling access to abortion a core legislative goal, overseeing the passage of scores of measures to that end. “I’ve never considered ‘pro-life’ to be a label or a position,” Mr. Boehner has said. “It’s just who I am.”

In one of his first moves as speaker, Mr. Boehner fought to end funding for abortions in the District of Columbia against a reluctant White House in the first near-shutdown standoff. He played a major role in forging the Pain-Capable Unborn Child Protection Act, which the House passed this year, and has a 100 percent anti-abortion voting record. He addresses abortion in speeches to Roman Catholic groups and refers often to the priests who formed his thinking.

“Mr. Boehner has always made protection of life a heartfelt priority,” said David O’Steen, the executive director of the National Right to Life Committee, who added that no other speaker had been such a strong supporter. “He has always supported and promoted pro-life legislation, he has repeatedly facilitated bringing pro-life legislation to the floor whenever feasible, he has attended and spoken at our convention, and he has marched for life, the first speaker to do so. We believe he cares deeply for unborn children and is doing everything he can to seek their protection.”

But the Planned Parenthood funding question has become a proxy for a minority of very conservative House Republicans who helped bring Mr. Boehner to power in the 2010 elections and have been working to push him to the right ever since.

The numbers opposing Mr. Boehner have grown in recent months, several Republican representatives and their staff members said, driven in large part by their own survival back in districts where all Republican establishment figures have been discredited. That movement has been fueled further by the popularity of Donald J. Trump, who has been critical of Washington leadership, and Carly Fiorina, who made a passionate case against Planned Parenthood at the Republican debate on Wednesday.

That thought has been echoed across the conservative news media and via the Twitter hashtag #fireboehner. Even if the abortion matter does not push Republicans to remove him, other fights may, including battles over the debt ceiling, reauthorizing funding for the Export-Import Bank and removing statutory budget caps.

Ultimately, it may be Democrats who provide the bulwark for Mr. Boehner to keep his job, if the matter actually comes to the floor of the House for a vote. But winning that way could further weaken his speakership as Congress heads into still more spending battles in December. Democrats may face a huge choice for a minority party: help weaken or even destroy Mr. Boehner, knowing his replacement could be even more uncompromising, or maintain the leadership they know and dislike.

“At this point, Mr. Boehner is either working on a deal with Democrats or planning his retirement,” said Representative Thomas Massie, Republican of Kentucky, who has been actively opposing Mr. Boehner. “It is obvious to everyone, including the speaker, that he has more than 29 defections. There are people who are already running for his seat right now.”

It could be that Mr. Boehner’s detractors are merely noisy and that their numbers are not sufficient to topple him.

It is the kind of fight that has not happened in modern history. Should Mr. Boehner be removed, a clear successor, who would need a majority of the entire House to rise in support, is not visible, and no legislative work could be done until one was selected.

An article on Friday about conservative lawmakers on the far right questioning John Boehner’s resolve to stand up to President Obama over federal funding for Planned Parenthood misstated the state that was represented by Nathaniel Banks, who was elected speaker in 1856 after a lengthy voting process. It was Massachusetts, not Maine.

A version of this article appears in print on , on Page A1 of the New York edition with the headline: Boehner, Strong Abortion Foe, Is Imperiled by the Like-Minded . Order Reprints | Today’s Paper | Subscribe